Gray Goo of Mid Summer

The high school student Kurashiki Manatsu (Midsummer) has one of the best kendo skills in Japan, but she is not good at studying.
Together with Tsumugi, an insect video creator, and Ayano, an urban legend expert and conspiracy theorist, she was about to attend
remedial classes on the first summer vacations day, but a Self-Defense Force helicopter suddenly landed in the schoolyard.
This was the beginning of a super dangerous and too hot summer vacation for Midsummer!